CS61B笔记 | Proj1A LinkedListDeque CS61B-Spring-2018

代码

/*链表双端队列*/  
  
public class LinkedListDeque<T> {  
  
    private IntNode sentinel;  
    private int size;  
  
    private class IntNode {  
        private T item;  
        private IntNode prev;  
        private IntNode next;  
  
        public IntNode(IntNode prev, T item, IntNode next) {  
            this.prev = prev;  
            this.item = item;  
            this.next = next;  
        }  
    }  
  
    public LinkedListDeque() {  
        sentinel = new IntNode(null, null, null);  
        sentinel.prev = sentinel;  
        sentinel.next = sentinel;  
    }  
  
    public void addFirst(T item) {  
        if (isEmpty()) {  
            sentinel.next = new IntNode(sentinel, item, sentinel.next);  
            sentinel.prev = sentinel.next;  
        } else {  
            sentinel.next = new IntNode(sentinel, item, sentinel.next);  
            sentinel.next.next.prev = sentinel.next;  
        }  
        size++;  
    }  
  
    public void addLast(T item) {  
        sentinel.prev.next = new IntNode(sentinel.prev, item, sentinel);  
        sentinel.prev = sentinel.prev.next;  
        size++;  
    }  
  
    public boolean isEmpty() {  
        return sentinel.next == sentinel && sentinel.prev == sentinel;  
    }  
  
    public int size() {  
        return size;  
    }  
  
    public void printDeque() {  
        IntNode ptr = sentinel.next;  
        while (ptr != sentinel) {  
            System.out.print(ptr.item + " " + "\n");  
            ptr = ptr.next;  
        }  
    }  
  
    public T removeFirst() {  
        if (!isEmpty()) {  
            T tmp = sentinel.next.item;  
            if (sentinel.next.next == sentinel) {  
                sentinel.next = sentinel.next.next;  
                sentinel.prev = sentinel.prev.prev;  
                sentinel.next.prev = sentinel;  
                size--;  
                return tmp;  
            } else {  
                sentinel.next = sentinel.next.next;  
                sentinel.next.prev = sentinel;  
                size--;  
                return tmp;  
            }  
        } else {  
            return null;  
        }  
    }  
  
    public T removeLast() {  
        if (!isEmpty()) {  
            T tmp = sentinel.prev.item;  
            IntNode intermediateNode = sentinel.prev.prev;  
            sentinel.prev.prev.next = sentinel;  
            sentinel.prev = intermediateNode;  
            size--;  
            return tmp;  
        } else {  
            return null;  
        }  
    }  
  
    public T get(int index) {  
        IntNode ptr = sentinel;  
        int tmp = 0;  
        while (ptr.next != sentinel) {  
            if (tmp == index) {  
                return ptr.next.item;  
            }  
            tmp++;  
            ptr = ptr.next;  
        }  
        return null;  
    }  
      
  
    public T getRecursive(int index) {  
        return getRecursive(sentinel, index, 0);  
    }  
  
    private T getRecursive(IntNode x, int index, int tmp) {  
        IntNode ptr = x;  
        if (ptr.next == sentinel) {  
            return null;  
        } else if (tmp == index) {  
            return ptr.next.item;  
        }  
        return getRecursive(ptr.next, index, tmp + 1);  
    }  
}